He said that only a few weeks ago, against the Titans in Week Three, could he play a full game without experiencing knee fatigue.

Growing pains in adjusting to an NFL offense aren’t atypical for a rookie receiver – and Allen, a third-round draftee, said he "messed up" routes in both practices and preseason games.

“You have to give credit to Keenan for growing up a little bit,” Whisenhunt said. “He’s not a finished product yet. He still has work to do. We got on him pretty hard about some things he was doing, and when he had a chance to step up in the Philadelphia game and make some plays, he did that. You can see him gain confidence that he could do it. The challenge for Keenan is to get into that pro mentality that you have to do it every day.”

Whisenhunt couldn’t name another NFL receiver who reminds him of Allen, who is 6-foot-2 and 211 pounds.

“If he continues to work and grow the way he is going right now," the coach said, "he has a chance to be pretty good. He could be one of those guys years down the road that I say, 'Keenan was pretty good.' ”